The subject invention is related to a rechargeable lithium battery used for mobile power supply, backup memory power supply, etc, and method of making same.
Due to the rapid technological development in the field of electronics in recent years, miniaturization of electronic devices have progressed, and as the power supply for such devices the demand for small, light weight, batteries having high energy density has been rising. As such a battery, the lithium battery using lithium as the negative electrode has received attention and research is being conducted world-wide. However, when metallic lithium was used for the negative electrode, through repeated charging and discharging, the lithium has become drawn out or branch-type crystals called lithium dendrites have formed on the surface of the lithium negative electrode to damage the shape of the lithium negative electrode, and, the charging cycle life was extremely short. And, this would finally cause the lithium falling off the negative electrode to penetrate through the separator and even cause internal shorting in the battery.
As one measure of resolving this problem, the use of lithium-aluminum alloy for the negative electrode is proposed in U.S. Pat. No. 4,874,680. Also, the use of a lead alloy with absorbed lithium as the negative electrode is proposed in the Japanese Opened-to-the-Public Patent Application SHO 57-141869. Furthermore, the superiority of niobium pentoxide as a compounding material with lithium for preventing the breakout of lithium dendrites is disclosed in U.S. Pat. No. 5,015,547.
In general, niobium pentoxide has different crystal types depending on its heat treatment temperature. At a heat treatment temperature of 500.degree. C. or less, the crystal type generally called T type is obtained; at heat treatment temperature of 700.degree. to 850.degree. C. the generally called T type; at heat treatment temperature of 850.degree. to 1100.degree. C. a mixture of T type and H type is obtained; at 1100.degree. C. or above the crystal type called the H type is obtained.
Yet, when niobium pentoxide is used as the negative electrode, it is not yet clear how the electrode characteristics change depending on the crystal types.